Electrical apparatus



INVENTORS alr/es F afm 2mes 7'.' orf G 5. #Wj ATTORNEY Filed sept. 22,1951 Feb. 13, 1934-.,

WITNESSES Patented Feb. 13, 1934 PATENT OFFICE 1,947,085 ELECTRICALAPPARATUS Charles F. Hill, Edgewood, and James T. Goff, Wilkinsburg,Pa., assignors to Westinghouse Electric and Manufacturing Company, a

ration of Pennsylvania como' Application September 22, 1931 Serial N0..564,280

6 Claims.

This invention relates to electrical apparatus in which the active partsare subject to heating and which is required to be insulated from thewalls of a surrounding tank or container.

The present invention is more particularly directed to a construction ofelectrical apparatus, such as transformers, in which novel means isemployed for insulating and cooling the apparatus.

It is common practice to immerse electrical apparatus, such astransformers, in an insulating and cooling oil. There are, however,limitations to the use of oil as an insulating and cooling material,because of the fire hazards that accompany its use and because of thenecessity of in specting the transformer from time to time to insurethat the oil is maintained at the proper level in the tank, and retainsits normal insulating characteristics. Under certain conditions ofoperation of transformers employing insulating oil, explosivehydrocarbon gases or hydrogen or a mixture thereof, may bev given offfrom the transformer oil which may unite with the oxygen of the air andform an explosive gaseous mixture. Such a mixture is especiallydangerous whenvthe transformer is located in an enclosure such as theroom of a building.

It is an object of our invention to provide a new material forinsulating electrical apparatus, such as transformers, that will reducefire hazards and be substantially explosion proof.

It is a further object of our invention to provide such an insulatingmaterial that possesses sufficiently high dielectric strength and highheat conductivity.

It is another object of our invention to provide an insulating materialfor surrounding the apparatus that is permanent in character and doesnot require frequent servicingy in order to maintain the desired qualityandy quantity of insulating material within the tank containing theapparatus.

In accomplishing the purpose of our invention, we dispense with theusual insulating mineral oil and substitute, therefore,.an\inorganicgranular or powdered material having high dielectric strength and highheat conductivity and impregnate this material with an insulating andheat J conducting material having a binding action. This material may bea polymerized vegetable oil, such as perilla, linseed oil, or tung oil,or a fusible salt, such as boric acid, potassium nitrate, or sodiumnitrate, or it may be a gum or synthetic resin that solidines in anon-porous condition, that is, without giving oir moisture, such ashalowax.

We prefer, however, to employ a polymerized vegetable oil, andparticularly, jelled tung oil.

'I'he single figure of the drawing is a side elevation partially insection, illustrating a transformer organized in accordance with ourinvention.

Referring to the drawing, a tank 1 is employed which contains thetransformer or other electrical apparatus, and, as illustrated,comprises a core 2 upon which is wound a primary winding 65 3 and asecondary winding 4. The primary winding is connected by means ofconductors 5 and 6 to the terminals '7 and 8, and the secondary winding4 is connected by means of conductors 9 and l0 to the terminals 11 and12. About the core and coils of the transformer, the electric insulatingmaterial 13. is placed and by means of this material the heat generatedin the core and coils of the transformer is conducted to the tank wall.

The refractory powdered or granular material, together with the bondingmaterial, may be placed in the tank in one of several ways. Tha twomaterials may be mixed and then molded in place in the tank, heat beingapplied during the molding operation, or the granular material may ilrstbe placed within the tank and the impregnating material forced throughthe spaces between the particles of the granular material and heatafterwards applied to solidify the impregnating material. Another methodof applying the insulating material to the transformer is to pour firstthe bonding fluid into the tank and then heat the granular material andpour this material in a heated condition into the bonding fluid. Thebonding fluid and granular material may be mixed by thoroughly stirringthe two materials together and then placing this mixture in the tank andheating it to between 150 C. and 200 C. for about five hours to producethe bonding action.

As a specic example of our invention, we pro-- pose to use quartz sandor quartz gravel as the inorganic granular material, either in apowdered or granular form, but a number of other materials, such aszirconium oxide, clay, alundum, carborundum or andralusite may be used.One or more of the above named materials may be employed for `theinsulating filler. Quartz sand or gravel is, however, preferred, becauseit has the highest heat conductivity and best dielectric characteristicsof any materials tested, is easi- 1y obtained and can be found inquantity with smooth rounded edges which is of value in producing a.mixture of high dielectric strength.

The bonding material or binder is added to the inorganic insulatingmaterial in order to ll the spaces between the particles and therebyimprove the heat conductivity and the electrical insulatingcharacteristics of the quartz sand or similar material. To obtain thehighest dielectric strength of the mixture, the bonding material used tofill the voids of the granular material should approach as near aspossible the specific inductive capacity of the granular material. It

is, however, also desirable that the insulation shall be mechanicallystrong and conduct heat readily from the transformer. With these severalobjectives in mind, it has been found that both organic and inorganicbonding materials are satisfactory, such materials as jelled Chinawoodoil or tung oil, sulphur boric acid, halowax or lead borate are found tobe satisfactory.

The dielectric strength of the jelled tung oil and quartz sand isapproximately one-half that of the tung oil itself, because of the greatdierence in specific inductive capacity of the tung oil and quartz. Theactual dielectric strength of the quartz is greater than that of theoil. In order to improve the dielectric strength of the tung oil andsand combination, it may be desirable to employ an insulating compoundformed of three materials. We have found that the dielectric strength ofthe resultant material is increased by using a rather coarse gravel andadding a fusible salt, such as boric acid, thereto heating the twomaterials together to the fusing point of the salt and stirring tothoroughly wet the gravel with the fused salt. This hot mixture is thenpoured into place in the transformer tank, thus allowing the fused saltto seal the joints or points of contact between the particles of gravelas it cools. This material is then impregnated with tung oil, which isjelled by heating. Bakelite varnish may be used in place of the boricacid to wet the gravel and bond it at the contact points betweenadjacent pebbles.

The tung oil seals the mass against moisture. A gum coating may be addedover the top of the mixture to aid in sealing it against moisture ifdesired.

Boric acid powder and sand or gravel may be mixed dry and poured intoplace in the tank, afterwards being heated to fuse the boric acid toallow the fused salt to seal the joints between the particles of sand orgravel, and the mixture afterwards impregnated with tung oil and jelledby further heating.

Since many modifications in the materials and methods of processing themmay be employed other than those described without departing from thespirit of our invention, we do not wish to be limited other than by thescope of the appended claims.

We claim as our invention:

1. In combination, a tank, electrical apparatus contained therein, andheat conducting and insulating material disposed between said apparatusand said tank comprising a mixture of quartz sand and an impregnatingjelled vegetable oil.

2. An insulating material for electrical apparatus including apulverulent granular solid insulating material mixed with a solidifyingbinder of jelled vegetable oil.

3. In combination, a container, electrical apparatus contained therein,and an insulating substance lling the space between said apparatus andthe Walls of said container comprising a granular ller and a jelledvegetable oil binder.

4. In combination, a tank, electrical apparatus contained therein, heatconducting and electric insulating material embedding said apparatus andsubstantially filling the space between the apparatus and said tank,said material comprising a pulverulent inorganic filler and a bindercomprising a polymerized vegetable oil binder.

5. An insulating material for electrical apparatus comprising a granularinorganic filler and a fusible salt fused and mixed with the filler toseal the points of contact between the particles thereof, and animpregnating binder of jelled vegetable oil.

6. The process of making. an insulating materal comprising heating amixture of a rather coarse quartz granules and a fusible salt to thefusing point of the salt and stirring to thoroughly wet the granuleswith the fused salt and seal the points of contact between theparticles, impregnating the resulting mixture with a binder including adrying vegetable oil, and then applying heat to solidify the mass.

CHARLES F. HILL. JAMES T. GOFF.

